Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats


I

Forging Steel.                                 133,                          |

f
be carefully built at  right angles ;   this   point, as   well   as that                          f

of the general straight ness of the shaft must be gauged with
square and straight-edge by the head forgeman, as the work
progresses.

By this time then our forging has reached the condition Hy
and as the sketch A, Fig, 126, shews us a solid collar, for the
purpose of coupling to another shaft, we must add this portion.
Slabs are again piled up as at j, Fig. 1260, heated and welded,
until sufficient staff has been worked together to form a small collar
K, and then the whole collar can be finished either by the slab
method, or scarfed bars (L) can be wrapped round the shaft and
thoroughly welded Finally the collar can be chipped down at M
to the correct length, and cut off entirely at N. There only
remains the porter end o, which may he finished by taking off
the handles, and clamping them at the collar end, then putting
the porter through the furnace till it protrudes at the further doorf
and after heating cutting it off to the length shewn on the drawing.
The shaft is then set aside to cool.

Steel Shafts are forged from ingots (obtained by any of the
processes mentioned in Chap. Ill), and being thus treated from a.
solid block, differ in no sense, except size, from the example shewn
in Fig. 119. Some makers prefer, after flattening the ingot to the
thickness and height of the crank webs, to set down the central
portion of the shaft, forging each web in the same plane; and
afterwards, to turn one web at right- angles to the other by
twisting the shaft; but there can be little doubt that this is an
objectionable method, and should never be resorted to. A good
deal of care, in the case of steel, should be taken to get rid of the
blow-holes previously mentioned as existing in the ingots, and as
simple hammering is usually insufficient, cogging is the operation
performed, which consists in partly punching the steel while hot
immediately over any portion where honeycombing is suspected—
a sort of kneading, in fact

After the careful description of the crank-shaft forging, a share
explanation will suffice for the following articles—Piston-rod with
Crpss-head, and a Connecting-rod. Whenever such forgings are
made of wrought iron they are built up from scrap as in the case
of the shaft, such scrap consisting of ail kinds of wrought iron>